Typhoid has broken out among Palestinians in the Yarmouk refugee camp in the Syrian capital of Damascus, the United Nations confirmed Wednesday. The camp has seen some of the fiercest fighting since the Syrian civil war broke out four years ago, and its residents have suffered from a crippling blockade by Assad government forces since 2013. 

“UNRWA [United Nations Relief and Works Agency] has had its first access to civilians from the besieged Palestinian refugee camp of Yarmouk, Damascus, since 8th June,” UNRWA spokesman Chris Gunness said in a statement, according to Ma’an News, a Palestinian news agency. “We can now confirm a typhoid outbreak among this U.N.-assisted population with at least six confirmed cases.”

Typhoid is a life-threatening illness caused by the bacteria Salmonella typhi, spread through consuming contaminated food or water. While about 21 million people are infected with typhoid each year in developing countries, it is usually rare in the Middle East. 

The U.N. is concerned as Palestinians in Yarmouk continue to face a humanitarian crisis thanks to the government siege. Since fighting broke out, more than 90 percent of the camp’s population has fled; it has dwindled from 160,000 people to just around 14,000. Human rights organizations have reported deaths resulting from food shortages and inadequate medical supplies, as the U.N. agency for Palestinian refugees has been unable to operate in Yarmouk since it was besieged in 2013.

The situation has deteriorated in recent months, as fighters with the Islamic State group, also known as ISIS or ISIL, have gained a foothold in the camp.

The U.N., unable to operate in the camp itself, was able to meet with residents who had fled Yarmouk to a nearby neighborhood. UNWRA has set up a mobile health clinic for Palestinians in that area, where aid workers were able to confirm at least six cases of the deadly bacteria.

In recent months, the agency has used the hashtag #SaveYarmouk and has set up a page on its website in an effort to raise awareness of the deteriorating situation in the camp.

“Never has the imperative for sustained humanitarian access been greater,” Gunness said.